The present invention refers to a class AB single-stage advanced operational amplifier.
The operating class of the operational amplifiers is defined according to the polarization of the active elements that supply power to the load and can be divided, among the various ones existing, into class A, in which the active elements always operate in a conduction zone and are polarized at about the center of it (for bipolar signals), class B, in which the active elements are polarized at the locking limit of the conduction zone, class AB, in which the active elements are weakly polarized within the conduction zone, and in class C, in which the active elements operate far from the conduction zone.
In particular, class AB has the characteristics of having reduced distortion for small signals, good operating efficiency, zero stand-by power and a low dissipation of the active elements, but with circuit architecture that provides for an input stage of the voltage decoupler type (source-follower for MOS technology, or emitter-follower for bipolar technology); it also has the problem of the doublet pole-zero introduced by such a stage that limits the band width available and considerably degrades the phase margin of the amplifier itself bringing it close to instability.
Class AB operational amplifiers are known that comprise an input stage of the voltage decoupler type (source follower for MOS technology, emitter follower for bipolar technology) and means for polarizing the amplifier itself, such as to introduce low frequency singularity capable of degrading the phase margin.
In view of the state of the technique described, the disclosed embodiment of the present invention provides an operational amplifier capable of reducing the effect of the doublet pole-zero introduced by the input stage.
A class AB single-stage operational amplifier is disclosed that includes a decoupler input stage for voltage signals, a voltage repeater stage, biasing means and means for the generation of bias current of the decoupler input stage, and a capacitive structure placed between the voltage decoupler stage and the voltage repeater stage so that the phase margin is increased.
In accordance with the embodiment of the present invention disclosed herein, a compensation technique can be made that is capable of reducing the effect of the pole-zero, thus increasing the phase margin of the operational amplifier, supplying a wider band width, and increasing, therefore, the stability of the system.